Positioner Isocenter Secondary Angle Attribute
| Tag | (0018,9464) |
|---|---|
| Type | Conditionally Required (1C) |
| Keyword | PositionerIsocenterSecondaryAngle |
| Value Multiplicity | 1 |
| Value Representation | Single (FL) |
Position of the X-Ray center beam for this projection in the isocenter reference system in the Z direction (deg).
See Section C.8.19.6.13.1.2 for further explanation.
Required if present and consistent in the contributing SOP Instances.
Section C.8.19.6.13.1.2
C.8.19.6.13.1.2 Positioner Coordinate System
The Positioner Coordinate System (Op, Xp, Yp, Zp) is defined as follows:
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Origin Op, is the origin of the Isocenter coordinate system O
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Xp axis is parallel to the horizontal scan-lines of the detector (rows). Positive direction from left to right of the detector plane looking towards the source.
-
Zp axis is parallel to the vertical scan-lines of the detector (columns). Positive direction from bottom to top of the detector plane looking towards the source.
-
Yp is the axis from the isocenter to the X-Ray source. Positive direction from the Isocenter to the X-Ray Source. This axis is so-called the X-Ray center beam.
Figure C.8.19.6-5. Positioner Coordinate System
Note
The quantities SID and ISO are specified by the Attributes Distance Source to Detector (0018,1110) and Distance Source to Isocenter (0018,9402) respectively.
The Positioner Coordinate System (Op, Xp, Yp, Zp) is characterized, with respect to the Isocenter Coordinate System (O, X, Y, Z), by two angles describing the X-Ray center beam, and a third angle describing the rotation of the X-Ray detector plane. These angles are relative to the Isocenter reference system, and independent from the patient position on the equipment.
Positioner Isocenter Primary Angle (0018,9463) (so-called Ap1 in Figure C.8.19.6-6) is defined in the plane XY, as the angle between the plane YZ and the plane YpZ. The axis of rotation of this angle is the Z axis. Angle from -Y to +X is positive. The valid range of this angle is -180 to +180 degrees.
Positioner Isocenter Secondary Angle (0018,9464) (so-called Ap2 in Figure C.8.19.6-6) is defined in the plane YpZ, as the angle of the X-Ray Center Beam (i.e., Yp) relative to the XY plane. The axis of rotation of this angle is perpendicular to the plane YpZ. Angle from the plane XY to +Z is positive. The valid range of this angle is -180 to +180 degrees.
Positioner Isocenter Detector Rotation Angle (0018,9465) (so-called Ap3 in Figure C.8.19.6-6 and in Figure C.8.19.6-7) is defined in the detector plane, as the angle of the vertical scan-lines of the detector (i.e., Zp) relative to the intersection between the detector plane and the plane YpZ. The sign of this angle is positive clockwise when facing on to the detector plane (see Figure C.8.19.6-7). The valid range of this angle is -180 to +180 degrees.
Figure C.8.19.6-6. Positioner Isocenter Angles
Figure C.8.19.6-7. Positioner Isocenter Detector Rotation Angle when Ap1 = 0 and Ap2 = 0